Halve and remove fruit from grapefruits and oranges. Cut peel into uniform 1/2" strips. Pare off white pith. Put in a saucepan with water enough to cover. Boil 5 minutes, drain, and repeat. (This debitters the peels.) Add 2 cups sugar. Cook until peels are transparent and sugar is absorbed (about 45 minutes), watching to avoid scorching. Spread a cookie sheet with 2 1/2 cups sugar. Roll the peels in sugar. Lay strips skin-side-up on a wire rack. Put waxed paper over them. Let rest 2-3 days. Melt chocolate in a double boiler. Dip ends of peels into chocolate. Let cool on rack. Store in an airtight box with waxed paper between layers.